Multi-layer loading tube for perforating gun

ABSTRACT

A perforating gun for perforating a casing of a well includes one or more shaped charges configured to perforate the casing; a loading tube configured to hold the one or more shaped charges; a housing having a cylindrical shape and configured to receive inside the loading tube and the one or more shaped charges; and a protective tube located in an annulus formed between the housing and the loading tube.

BACKGROUND Technical Field

Embodiments of the subject matter disclosed herein generally relate to a perforating gun for making perforations into a casing of a well, and more specifically, to a multi-layer loading tube that holds the shaped charges and prevents damage to a housing of the perforating gun.

Discussion of the Background

In the oil and gas field, once a well is drilled to a desired depth H relative to the surface, and the casing protecting the wellbore has been installed and cemented in place, it is time to connect the wellbore to the subterranean formation to extract the oil and/or gas. This process of connecting the wellbore to the subterranean formation may include a step of plugging a previously fractured stage of the well with a plug, a step of perforating a portion of the casing, which corresponds to a new stage, with a perforating gun string such that various channels are formed to connect the subterranean formation to the inside of the casing, a step of removing the perforating gun string, and a step of fracturing the various channels of the new stage. These steps are repeated until all the stages of the formation are fractured.

During the perforating step for a given stage, one or more perforating guns of the perforating gun string are used to create perforation clusters in the multistage well. Clusters are typically spaced along the length of a stage (a portion of the casing that is separated with plugs from the other portions of the casing), and each cluster comprises multiple perforations (or holes). Each cluster is intended to function as a point of contact between the wellbore and the formation. Each perforation is made by a corresponding shaped charge, which is located inside the housing of the perforating gun. The shaped charge includes an explosive material which when ignited, melts a lining of the shaped charge and generates a travelling melted jet. The travelling melted jet is projected outward from the shaped charge, to make a perforation into the housing of the perforating gun and then a perforation into the casing of the well, to establish the fluid communication between the oil formation outside the well and the bore of the casing.

After each stage is perforated, a slurry of proppant (sand) and liquid (water) is pumped into the stage at high rates and then, through the perforation holes, into the formation, with the intent of hydraulically fracturing the formation to increase the contact area between that stage and the formation. A typical design goal is for each of the clusters to take a proportional share of the slurry volume, and to generate effective fractures, or contact points, with the formation, so that the well produces a consistent amount of oil cluster to cluster and stage to stage.

However, due to the improved efficiency of the shaped charges and their increased firing angle, the traveling melted jet may severely damage the housing of the perforating gun, in addition to the intended perforation, so that the housing may split or become so deformed that would inhibit the ability to move the used up perforating gun within the casing. In other words, as shown in FIG. 1, a perforating gun string 110, that includes first and second perforating guns 112 and 114, is lowered into a well 116, with a wireline 118. The wireline 118 is connected to a derrick 120, that is controlled by a controller 122, for example, a computing device. The derrick 120 and the controller 122 are located at the surface 124. The first and second perforating guns 112 and 114 sit on the casing 130 of the well 116 and each perforating gun may include plural shaped charges 112A and 114A, respectively. While the shaped charges 112A of the first perforating gun 112 have not yet been detonated, the shaped charges 114A of the second perforating gun 114 have been detonated. In this regard, it is noted that the housing 115 of the second perforating gun 114 has various holes, which correspond to each of the fired shaped charges. Further, FIG. 1 shows that the margins 132 of a given hole formed in the housing 115, which is a metal cylinder, have suffered severe damage due to the detonation of the charges and these margins are now bent and in contact with the casing 130 of the well. This means that either there is a large friction between the housing 115 and the casing 130, or the entire second perforating gun 114 is stuck in the casing 130. This is undesirable because the first perforating gun 112 needs to be moved to its desired location relative to the oil and has formation 134, and this action now cannot be completed because of the damaged housing 115.

Such severe deformation of the housing 115 of the perforating gun 114 is possible to be prevented if the thickness of the housing is increased or the housing is made of multiple layers. However, these approaches impact the shaped charge's performance and add weight, expense and complexity to the perforating gun, all of which are undesirable.

Thus, there is a need for a new approach for preventing the housing of the perforating gun from deforming or breaking into pieces so that the perforating gun does not become stuck in the casing.

SUMMARY

According to an embodiment, there a perforating gun for perforating a casing of a well, and the perforating gun includes one or more shaped charges configured to perforate the casing, a loading tube configured to hold the one or more shaped charges, a housing having a cylindrical shape and configured to receive inside the loading tube and the one or more shaped charges, and a protective tube located in an annulus formed between the housing and the loading tube.

According to another embodiment, there is a perforating gun for perforating a casing of a well. The perforating gun includes one or more shaped charges configured to perforate the casing, a loading tube configured to hold the one or more shaped charges, a protective tube located around the loading tube and configured to receive the one or more shaped charges in corresponding holes, and a housing located around the protective tube.

According to still another embodiment, there is a method for protecting a housing of a perforating gun from excessive damage. The method includes placing one or more shaped charges into a loading tube of a perforating gun, covering the loading tube with a protective tube, and loading the loading tube with the protective tube into a housing of the perforating gun. The protective tube is located in an annulus formed between the loading tube and the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

FIG. 1 illustrates a perforating gun having a housing damaged by a detonated shaped charge so that the perforating gun cannot move through the casing of the perforated well;

FIG. 2 illustrates a perforating gun having a protective tube located in an annulus defined by a loading tube and the housing, to protect the housing from excessive damage from the shaped charges;

FIG. 3 shows a cross-section through the perforating gun of FIG. 2, showing the protective tube disposed inside the housing, and fully enclosing the loading tube;

FIG. 4 shows another implementation of the perforating gun of FIG. 2, where the protective tube is formed of plural elements, each element enclosing a corresponding portion of the loading tube;

FIG. 5 shows a cross-section of the perforating gun having legs that hold the protective tube around the loading tube;

FIG. 6 shows end plates of the perforating gun that have slots for receiving corresponding tabs of the protective tube;

FIG. 7 shows an embodiment in which the protective tube is hold exclusively by the shaped charges around the loading tube;

FIG. 8 shows the protective tube being made to include plural discrete tubes; and

FIG. 9 is a flow chart of a method for adding a protective tube to a perforating gun for protecting the housing from excessive damage.

DETAILED DESCRIPTION

The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a perforating gun used for perforating a casing in a well. However, the embodiments discussed herein may be used for guns in another context.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

According to an embodiment, a perforating gun includes, in addition to a loading tube that holds the shaped charges, and a housing that encapsulates the shaped charges, a protective tube that is provided between the loading tube and the casing. Thus, a multi-layered loading tube includes an existing loading tube and the protective tube. The protective tube is configured to limit the possibility of the melted jet generated by the shaped charges to severely damage the housing except for the intended location of the perforation. In other words, the protective tube acts as a shield protecting the housing of the perforating gun from the shaped charge detonation effects which may include charge fragments, heat, loading tube debris, pressure spikes, or other debris generated during the detonation process.

More specifically, as shown in the embodiment of FIG. 2, a perforating gun 200 includes one or more shaped charges 210 located around and partially within a loading tube 220. The loading tube 220 may have plural holes 222 distributed with a desired pattern and the plural holes 222 are configured to receive the plural shaped charges 210. In one embodiment, each shaped charge 210 is fixedly attached to a corresponding hole 222 formed into the loading tube 220. The loading tube 220 and the shaped charges 210 are fully enclosed (except for their ends) by the housing 230. The housing 230 separates the fluids from the well from the shaped charges and the other components of the perforating gun 200, for example, the detonation cord 212. The housing 230 may be processed to have internal or external scallops or both, which correspond to the shaped charges, so that the melted jet generated by a shaped charge can easily make a perforation into the housing. FIG. 2 shows only external scallops 232. However, none of the scallops extends from one side of the housing to the other side so that the fluid from the well is prevented from entering inside the perforating gun.

FIG. 2 also shows a protective tube 240, which in this embodiment is concentric to the loading tube 220 and to the housing 230. The protective tube 240 is thus located in the annulus 242 formed by the loading tube 220 and the housing 230. Note that each of the loading tube 220, the protective tube 240, and the housing 230 has a cylindrical shape in this embodiment. While FIG. 2 shows that the three cylinders are concentrical to each other, in one application, the loading tube and/or the protective tube are not concentric to the housing or to each other.

The protective tube 240 has plural through holes 244 that correspond to the plural shaped charges 210. For example, as shown in FIG. 2, each shaped charge 210 has a lip 214 that protrudes through the holes 244 in the protective tube 240. FIG. 3 shows a longitudinal cross-section through the perforating gun 200. It is noted that the housing 230 has threads 234A and 234B at each end 230A and 230B, so that the housing 230 can be attached to a sub 300, for being attached to another perforating gun (not shown). FIG. 3 also shows end plates 236A and 236B that close the ends of the loading tube 220 and the protective tube 240 so that the inside of the loading tube 220 is fluidly insulated from the outside of the gun. FIG. 3 shows that the detonation cord 212 exits through the end plates 236A and 236B, so that it can be connected to a corresponding detonator 310, which can be placed either inside the housing 230, or inside the sub 300. In one application, the detonator 310 may be placed inside the loading tube 220, in which case the element 212 in FIG. 3 is an electrical connection, for example, a bulkhead assembly having one or more electrical connections. The loading tube 220 is not visible in FIG. 3 because it sits completely inside the protective tube 240. In one application, the detonator 310 is placed inside the housing, but outside the protective tube 240.

In another embodiment, the protective tube 240 is not continuous, i.e., it does not extend over the entire length of the loading tube 220, as shown in FIG. 4. In this embodiment, the protective tube 240 includes plural elements 240-1 and 240-2, each fully enclosing only a corresponding portion of the loading tube 220. The plural elements 240-1 and 240-2 (only two are shown in the figure for simplicity, but their number is not limited, only by the length of the loading tube) are shaped as cylinders. FIG. 4 shows that only a portion of the loading tube 220 not being covered by the elements 240-1 and 240-2. However, in one embodiment, plural portions of the loading tube are not covered by the elements of the protective tube 240.

The protective tube 240 may be attached to the interior of the perforating gun in various ways. For example, FIG. 5 shows the protective tube 240 being placed around the loading tube 220 and having plural legs (e.g., screws or other fixtures) 500 that enter through the protective tube 240 and sit on the outer surface of the loading tube 220. The leg 500 has a tip portion 500A that sits in direct contact with the outer surface of the loading tube 220 and a head portion 500B that is located in the external annulus 242A, formed between the protective tube 240 and the housing 230. Note that the leg 500 extends throughout the wall of the protective tube 240 so that the tip portion 500A is located in the internal annulus 242B, formed between the protective tube 240 and the loading tube 220. The head portion 500B may have a rotating mechanism 502, for example, a handle or a groove 502 that is configured to engage a screwdriver or another tool. Thus, the person that assemblies the perforating gun can adjust the amount of the leg 500 that is located inside the internal annulus 242B, to effectively adjust the position of the protective tube 240 relative to the loading tube 220, along a radial direction R. By operating three legs 500, the two cylindric elements may be made concentric to each other. In one embodiment, each end of the protective tube 240 may be provided with the three legs 500.

In another embodiment, as illustrated in FIG. 6, the end plates 236A and 236B (only one is shown for simplicity) may have slots 600 that are configured to receive tabs 610 that are provided at each end 240A and 240B of the protective tube 240. In this way, the protective tube is connected to the end plates and does not touch the loading tube 220 or the housing 230 and also does not need the legs 500. The tabs 610 may be formed in any shape. In one embodiment, no tabs are necessary as the protective tube 240 can be attached with bolts or screws directly to the side plates. In one application, the protective tube may be welded to the end plates. The loading tube 220 may also be connected to the end plates in the same manner as discussed above. In yet another embodiment, the protective tube 240 may be bolted or snapped onto the loading tube 220. Any of these means may be combined for a given perforating gun.

In yet another embodiment, the shaped charges 210 are used to hold the protective tube 240 away from the loading tube 220, as shown in FIG. 7. In other words, there is no leg, bolt, screw or metal part present between the protective tube 240 and the loading tube 220, except for the shaped charges 210. In yet another embodiment, the protective tube 240 may be attached to the housing 230, for example, using wings attached to the exterior of the protective tube 240 and these wings may be configured to engage with corresponding locks provided on the interior surface of the housing 230.

The spacing between the protective tube 240 and the loading tube 220 may be selected to be between zero and several mm, depending on the gun diameter and other design parameters associated with the shaped charges. In one embodiment, the gap between the two tubes may be even larger than several mm. The loading tube, the protective tube and the housing may be made of various materials. For example, all these elements may be made of steel or similarly strong materials. In one application, these elements may be made of different materials, for example, the housing may be made of steel and the loading tube and the protective tube may be made of a composite material.

By making the loading tube to be a multi-layer loading tube, i.e., to include the additional protective tube, the housing of the perforating gun is protected from severe damage with minimal additional material and expense and without adding any material to the housing, thus without changing the mass or thickness of the housing. Therefore, the performance of the shaped charges is not affected by the addition of the protective tube.

In yet another embodiment, the protective tube 240 may include two or more tubes of varying thicknesses, as illustrated in FIG. 8. For example, the protective tube 240 may have a first tube 810 having a first thickness and a second concentric tube 820 having a different thickness. More than two tubes may be used. The first and second tubes may be in direct contact or have a small annulus between them. The first and second tubes may be made from the same material or different materials.

A method for protecting a housing of a perforating gun from excessive damage is now discussed with regard to FIG. 9. The method includes a step 900 of placing one or more shaped charges into a loading tube of a perforating gun, a step 902 of covering the loading tube with a protective tube, and a step 904 of loading the loading tube with the protective tube into a housing of the perforating gun. The protective tube is located in an annulus formed between the loading tube and the housing.

The disclosed embodiments provide methods and systems for adding a protective tube to a loading tube, between the loading tube and the housing of a perforating gun, for minimizing the risk of severely damaging the housing so that the perforating gun can still move through the casing of the well after the shaped charges are fired. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. 

What is claimed is:
 1. A perforating gun for perforating a casing of a well, the perforating gun comprising: one or more shaped charges configured to perforate the casing; a loading tube configured to hold the one or more shaped charges; a housing having a cylindrical shape and configured to receive inside the loading tube and the one or more shaped charges; and a protective tube located in an annulus formed between the housing and the loading tube.
 2. The perforating gun of claim 1, wherein the loading tube, the protective tube, and the housing are concentric to each other.
 3. The perforating gun of claim 1, wherein the protective tube fully encircles the loading tube.
 4. The perforating gun of claim 1, wherein the protective tube includes plural discrete sections, each section fully enclosing a corresponding portion of the loading tube.
 5. The perforating gun of claim 1, wherein the protective tube has plural holes, each hole being configured to receive a corresponding shaped charge of the one or more shaped charges.
 6. The perforating gun of claim 1, wherein the housing has plural scallops, and the protective tube has plural holes, and each hole is radially aligned with a corresponding scallop.
 7. The perforating gun of claim 1, wherein the protective tube is located so that there is a first annulus between the loading tube and the protective tube and a second annulus between the protective tube and the housing.
 8. The perforating gun of claim 1, further comprising: plural legs that extend throughout an entire wall of the protective tube to contact the loading tube, wherein the plural legs maintain the protective tube centered around the loading tube.
 9. The perforating gun of claim 1, further comprising: end plates that attach to the loading tube, the end plates having one or more slots so that tabs of the protective tube enter the one or more slots and the protective tube is maintained around the loading tube without touching the loading tube.
 10. The perforating gun of claim 1, wherein only the one or more shaped charges holds the protective tube around the loading tube.
 11. The perforating gun of claim 1, wherein the protective tube includes two or more concentric tubes having different thicknesses or made of different materials.
 12. The perforating gun of claim 1, further comprising: a detonator cord that connects to the one or more shaped charges; and a detonator configured to ignite the detonation cord, wherein the detonator is located inside the housing but outside the protective tube.
 13. The perforating gun of claim 1, wherein the protective tube is configured to not interfere with a melted jet produced by the one or more shaped charges.
 14. A perforating gun for perforating a casing of a well, the perforating gun comprising: one or more shaped charges configured to perforate the casing; a loading tube configured to hold the one or more shaped charges; a protective tube located around the loading tube and configured to receive the one or more shaped charges in corresponding holes; and a housing located around the protective tube.
 15. The perforating gun of claim 14, wherein the loading tube, the protective tube, and the housing are concentric to each other.
 16. The perforating gun of claim 14, wherein the protective tube is located so that there is a first annulus between the loading tube and the protective tube and a second annulus between the protective tube and the housing.
 17. The perforating gun of claim 14, further comprising: plural legs that extend throughout an entire wall of the protective tube to contact the loading tube, wherein the plural legs maintain the protective tube centered around and radially distanced from the loading tube.
 18. The perforating gun of claim 14, further comprising: end plates that attach to the loading tube, the end plates having one or more slots so that tabs of the protective tube enter the one or more slots and the protective tube is maintained around the loading tube without touching the loading tube.
 19. A method for protecting a housing of a perforating gun from excessive damage, the method comprising: placing one or more shaped charges into a loading tube of a perforating gun; covering the loading tube with a protective tube; and loading the loading tube with the protective tube into a housing of the perforating gun, wherein the protective tube is located in an annulus formed between the loading tube and the housing.
 20. The method of claim 19, further comprising: centering the protective tube around the loading tube. 